The present invention relates to a virtual private network connecting system for connecting a plurality of private branch exchange (PBX) units accommodated in a public network by specifying numbers as if they were operated in a private network.
Private communication networks have become more and more important to efficiently perform business activities. The private communication can be conducted through public networks, but private networks can also be established such that a corporate private network, for example, a local area network, is configured using leased lines of common carriers as exclusive inter-office lines. In such private networks, inter-office communication can be made by dialing a private office number assigned to each office and an extension number of each office.
Private networks reduce the total amount of charges on long distance calls. However, they require various kinds of units and operations, expenses for equipment and maintenance, and personnel involved. Therefore, a virtual private network has been developed in order to establish a virtual network for private use using public networks without providing leased lines. The virtual private network is explained by referring to FIG. 1.
FIG. 1 is a block diagram for explaining the virtual private network of the prior art technology.
In FIG. 1, a plurality of PBX units 1 (each of them is designated 1-1, 1-2, . . . ) each belonging to the same company are connected to a public network 2 through office lines 3 each having a unique subscriber number SN assigned by the public network 2.
The public network 2 provides a virtual private network for connecting the PBX units 1 using private office numbers ON exclusively used in the company. To realize the service, the public network 2 has a specific switching unit 21-0 provided with a virtual private network center 22.
When an extension 4-1 accommodated in any PBX unit 1-1 issues a call and dials an identification number for the virtual private network service, a private office number ON of a destinating PBX 1-2, and a called extension number EN, the originating PBX unit 1-1 connects the call to an office line 3-1 and sends the identification number, the private office number ON and the extension number EN to a switching unit 211.
The switching unit 21-1 accommodating the originating PBX unit 1-1 recognizes that the PBX unit 1-1 is provided with the virtual private network service, and transmits the private office number ON to the virtual private network center 22 through the public network 2.
The virtual private network center 22 is provided with a function of converting a private office number ON assigned to each PBX unit 1 to a subscriber number SN, converts the transmitted private office number ON to the subscriber number SN, and sends it back to the originating switching unit 1-1. Afterwards, assuming that the subscriber number SN sent back from the virtual private network center 22 is received by the switching unit 21-1, the extension number EN received from the originating PBX unit 1-1 to specify the extension 4-2 is transmitted to the destination PBX unit 1-2 after connecting, according to the well-known procedure, the originating PBX unit 1-1 to the destination PBX unit 1-2 through the public network 2.
As described above, the conventional public network is provided with the virtual private network center 22 in order to realize a virtual private network service, and the virtual private network center 22 converts a private office number ON sent from the originating PBX unit 1-1 to a subscriber number SN. Therefore, a virtual private network service may not be offered to a public network 2 in which a virtual private network center 22 is not installed.